When God made this promise to Cyrus, He was
speaking of material treasures from lands of darkness that Cyrus would
conquer. But we are not doing violence to the verse when we take it and
apply it in a spiritual sense.

There are treasures that are discovered in the
dark nights of life that are never found in days of unrelieved sunshine.

For instance, God can give songs in the darkest night (Job 35:10) that would never have been sung if life were completely devoid of trials. That is why the poet wrote:

And many a rapturous minstrel among those sons of LightWill say of his sweetest music "I learned it in the night;"And many a rolling anthem that fills the Father's homeSobbed out its first rehearsal in the shade of a darkened room.

There is the darkness of what J. Stuart Holden
calls "life's inexplicable mysteries - the calamities, the
catastrophes, the sudden and unexpected experiences which have come
into life, and which all our forethought has not been sufficient to
ward off; and life is dark because of them - sorrow, loss,
disappointment, injustice, misconception of motive, slander." These are
often the things that make life dark.

Humanly speaking, none of us would choose this
darkness, and yet its benefits are incalculable. Leslie Weatherhead
wrote, "Like all men, I love and prefer the sunny uplands of
experience, when health, happiness and success abound, but I have
teamed far more about God and life and myself in the darkness of fear
and failure than I have ever learned in the sunshine. There are such
things as the treasures of darkness. The darkness, thank God, passes.
But what one learns in the darkness, one possesses for ever."